Charcoal
Charcoal is a lightweight black carbon residue produced by strongly heating wood in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, called charcoal burning, often by forming a charcoal kiln, the heat is supplied by burning part of the starting material itself, with a limited supply of oxygen. The material can also be heated in a closed retort. Modern charcoal briquettes used for outdoor cooking may contain many other additives, e.g. coal.
The early history of wood charcoal production spans ancient times, rooted in the abundance of wood in various regions. The process typically involves stacking wood billets to form a conical pile, allowing air to enter through openings at the bottom, and igniting the pile gradually. Charcoal burners, skilled professionals tasked with managing the delicate operation, often lived in isolation to tend their wood piles. Throughout history, the extensive production of charcoal has been a significant contributor to deforestation, particularly in regions like Central Europe. However, various management practices, such as coppicing, aimed to maintain a steady supply of wood for charcoal production. The scarcity of easily accessible wood resources eventually led to the transition to fossil fuel equivalents like coal.
Modern methods of charcoal production involve carbonizing wood in retorts, yielding higher efficiencies compared to traditional kilning methods. The properties of charcoal depend on factors such as the material charred and the temperature of carbonization.
Charcoal finds diverse applications, including metallurgical fuel in iron and steel production, industrial fuel, cooking and heating fuel, reducing agent in chemical processes, and as a raw material in pyrotechnics. It is also utilized in cosmetics, horticulture, animal husbandry, medicine using activated charcoal, and environmental sustainability efforts, such as carbon sequestration.
However, the production and utilization of charcoal can have adverse environmental impacts, including deforestation and emissions. Illegal and unregulated charcoal production, particularly in regions like South America and Africa, poses significant challenges to environmental conservation efforts.
History
Charcoal pile
The production of wood charcoal in locations where there is an abundance of wood dates back to ancient times. It generally began with piling billets of wood on their ends to form a conical pile. Openings were left at the bottom to admit air, with a central shaft serving as a flue. The whole pile was covered with turf or moistened clay. The firing began at the bottom of the flue, and the fire gradually spread outward and upward.The traditional method in Britain used a charcoal pile or clamp. This was essentially a pile of wooden logs leaning in a circle against a chimney. The chimney consisted of 4 wooden stakes held up by some rope. In the clamp too the logs were completely covered with soil and straw allowing no air to enter. It must be lit by introducing some burning fuel into the chimney. The logs burned slowly and transformed into charcoal over a period of 5 days. If the soil covering became torn or cracked by the fire, additional soil was placed on the cracks. Once the burn was complete, the chimney was plugged to prevent air from entering.
Charcoal burners
The true art of this production method was in managing the sufficient generation of heat, by combusting part of the wood material, and the transfer of the heat to the wood in the process of being carbonized. The operation was so delicate that it was generally left to colliers. They often lived alone in small huts to tend their wood piles. For example, in the Harz Mountains of Germany, charcoal burners lived in conical huts called Köten which still exist today.Low efficiency and harmful emissions
The success of the operation depends upon the rate of the combustion. Under average conditions wood yields about 60% charcoal by volume, or 25% by weight; small-scale production methods often yield only about 50% by volume, while large-scale methods enabled higher yields of about 90% by the 17th century. A strong disadvantage of this production method is the huge amount of emissions that are harmful to human health and the environment. As a result of the partial combustion of wood material, the efficiency of the traditional method is low.Peak of production and decline
Deforestation and scarcity
The massive production of charcoal was a major cause of deforestation, especially in Central Europe. Complaints about shortages may stem from over-exploitation or the impossibility of increasing production to match growing demand. In England, many woods were managed as coppices, which were cut and regrown cyclically, so that a steady supply of charcoal was available. But the increasing scarcity of easily harvested wood was a major factor behind the switch to fossil fuel equivalents, mainly coal and brown coal for industrial use.By-product of wood tar production
In Finland and Scandinavia, charcoal was considered the by-product of wood tar production. The best tar came from pine, thus pinewoods were cut down for tar pyrolysis. The residual charcoal was widely used as substitute for metallurgical coke in blast furnaces for smelting. Tar production led to rapid local deforestation. The end of tar production at the end of the 19th century resulted in rapid re-forestation of affected areas.Charcoal briquette
The American form of the charcoal briquette was first invented and patented by Ellsworth B. A. Zwoyer of Pennsylvania in 1897 and was produced by the Zwoyer Fuel Company. The process was further popularized by Henry Ford, who used wood and sawdust byproducts from automobile fabrication as a feedstock. Ford Charcoal went on to become the Kingsford Company.Production methods
The modern process of carbonizing wood, either in small pieces or as sawdust in cast iron retorts, is extensively practiced where wood is scarce, and also for the recovery of valuable byproducts, which the process permits. The question of the temperature of the carbonization is important; according to J. Percy, wood becomes brown at, a deep brown-black after some time at, and an easily powdered mass at. Charcoal made at is brown, soft and friable, and readily inflames at ; made at higher temperatures it is hard and brittle, and does not fire until heated to about.Modern methods employ retorting technology, in which process heat is recovered from, and solely provided by, the combustion of gas released during carbonization. Yields of retorting are considerably higher than those of kilning, and may reach 35%-40%.
The properties of the charcoal produced depend on the material charred. The charring temperature is also important. Charcoal contains varying amounts of hydrogen and oxygen as well as ash and other impurities that, together with the structure, determine the properties. The approximate composition of charcoal for gunpowders is sometimes empirically described as C7H4O.To obtain a coal with high purity, source material should be free of non-volatile compounds.
Wood charcoal is obtained as the residue by destructive distillation of wood such that the products are:
- Liquid products – pyroligneous acid and wood tar
- Gaseous products – wood gas
- Residual product – wood charcoal
Types
- Common charcoal is made from peat, coal, wood, coconut shell, or petroleum.
- Sugar charcoal is obtained from the carbonization of sugar and is particularly pure. It is purified by boiling with acids to remove any mineral matter and is then burned for a long time in a current of chlorine to remove the last traces of hydrogen. It was used by Henri Moissan in his early attempt to create synthetic diamonds.
- Activated charcoal is similar to common charcoal but is manufactured especially for medical use. To produce activated charcoal, common charcoal is heated to about in the presence of an inert gas, causing the charcoal to develop many internal spaces, or "pores", which help the activated charcoal to trap chemicals. Impurities on the surface of the charcoal are also removed during this process, greatly increasing its adsorption capacity.
- Lump charcoal is a traditional charcoal made directly from hardwood material. It usually produces far less ash than briquettes.
- Japanese charcoal has had pyroligneous acid removed during the charcoal making; it therefore produces almost no smell or smoke when burned. The traditional charcoal of Japan is classified into three types:
- *White charcoal is hard and produces a metallic sound when struck.
- *
- *Ogatan is a more recent type made from hardened sawdust.
- Pillow shaped briquettes are made by compressing charcoal, typically made from sawdust and other wood by-products, with a binder and other additives. The binder is usually starch. Briquettes may also include brown coal, mineral carbon, borax, sodium nitrate, limestone, raw sawdust, and other additives.
- Sawdust briquette charcoal is made by compressing sawdust without binders or additives. It is the preferred charcoal in Taiwan, Korea, Greece, and the Middle East. It has a round hole through the center, with a hexagonal cross-section. It is used primarily for barbecue as it produces no odor, no smoke, little ash, high heat, and has a long burning time.
- Extruded charcoal is made by extruding either raw ground wood or carbonized wood into logs without the use of a binder. The heat and pressure of the extruding process hold the charcoal together. If the extrusion is made from raw wood material, the extruded logs are subsequently carbonized.
Uses